The present invention relates to a belt or chain tensioner for motorcycles and automobiles and, more particulary, to a tensioner for tensioning a drive a chain or belt for driving camshaft of an engine.
A conventional tensioner, such as a belt tensioner or a chain tensioner is used to apply constant tension on a belt or chain even when the belt or chain looses predetermined tension due to elongation or slackening caused by wear or friction. For this reason, it is preferable that the tensioner be kept advanced at all times in a tensioning direction and that it have characteristics of a rigid object against a counterforce in a direction opposite the tensioning direction. FIG. 5 shows a vertical section of a conventional tensioner.
The tensioner comprises a casing 1 with a housing 1a formed in an axial direction, a rotational cylinder 2 inserted rotatably in said housing, a tension rod 3 engaged with a threaded portion of the rotational cylinder 2, and a torsion spring 4 inserted externally on the rotational cylinder 2. One end 4a of the spring is inserted in a slit 2a formed on the rear end of rotational cylinder 2, and other end 4b is inserted in a long groove 1b formed on the front portion of housing 1a for driving the rotational cylinder 2. A seal bolt 6 is screwed on the rear end of the casing. The top of said tension rod 3 is covered with a cap 8 fixed with a spring pin 7, whereby a chain or belt is tensed directly or indirectly to keep constant tension. The tension rod 3 is externally round and diametrically has two plain surfaces. Tension rod 3 is inserted freely in a corresponding slot of same shape formed in the bearing 9 so as not to turn, whereby the rotating force of the rotational cylinder 2 can be converted into an urging force.
This type of tensioner can be applied with a predetermined torsional torque by using a flat driver inserted through threaded hole on the rear end of the tensioner after mounting the component in the housing of casing. The threaded hole can then be hermetically closed with an "O" ring and the seal bolt. Thus the tensioner may be mounted, for example, on the outer wall of equipment, such as engine body, by inserting the front portion of the casing so that the cap of tension rod may work to keep constant tension on chain or belt by means of the restoring force of the torsion spring.
The tensioner works satisfactorily when mounted. However it is not easy to mount components, such as a tension rod, a rotational cylinder and a torsion spring in the tensioner housing. Therefore a ring groove of small diameter is formed between the cylinder portion and threaded portion so that a flat washer 10 may be freely mounted so as to mount a collar 11 between the bearing 9 and the flat washer 10. In this way, movement of the rotational cylinder 2, tension rod 3 and the torsion spring 4 in the axial direction can be prevented by the flat washer 10, collar 11, bearing 9 and the snap ring 12.
Hereinafter the problems to be solved by the present invention will be explained. In the conventional belt or chain tensioner, when the torsion spring 4 is wound to get torsional torque, the wire end 4b used to penetrate into the gap between the flat washer 10 and the rotational cylinder 2 sometimes impedes the normal function of the torsion spring 4 or the normal rotation of the rotational cylinder 2. This is because the torsion spring 4 extends in an axial direction when wound and, at the same time, eccentric movement can occur, causing the problems aforementioned. Then, it is effective to make the gap between the collar 11 and the flat washer 10 as small as possible, but it is very hard to reduce this gap ignoring the diameter of wire material.